The present invention relates to pharmaceutical compositions. In particular, the invention relates to a solution of etoposide in dimethylisosorbide (DMI).
Etoposide is a semi-synthetic product derived from podophyllotoxin. The material is identified by the chemical name 4'-demethylepipodophyllotoxin-9-(4,6-O(R)-ethylidine-.beta.-D-glucopyranos ide). It is approved by the Federal Food and Drug Administration for use in the treatment of refractory testicular cancer and small cell lung cancer and is currently being marketed under the tradename VePesid.RTM. as an injection solution containing for each ml, 20 mg of etoposide activity (PDR, 42nd Ed., pp. 779-80). The commercial solution is diluted to a manufacturer recommended concentration with an aqueous parenteral vehicle such as 0.9% NaCl, U.S.P. or 5% Dextrose for Injection, U.S.P. before administration by slow intravenous infusion. Etoposide is only sparingly soluble in water, its solubility in water being about 0.1 mg/ml. Thus, in order to prepare a solution of etoposide, an organic solvent or a mixture of organic solvents must be used. The choice of a suitable organic solvent for preparing pharmaceutical dosage forms is further limited to those that have high physiological safety. The marketed etoposide product for parenteral administration is contained in a multi-solvent system.
Etoposide has also been administered to patients via the oral route, either in capsules or as a solution; however, etoposide oral bioavailability is only about 50% of that found after intravenous administration (D'Incalci, M. Cancer Chemother Pharmacol, 7:141-145, 1982; Stewart, D. J. Cancer Treat Rep, 69:269-273, 1985; and Clark, P. I. and Slevin, M. L., Clin. Pharmacokinet, 1987, 12:223-252 at 238-240). Both U.S. Pat. No. 4,713,246 and U.S. Pat. No. 4,734,284 postulate that the low bioavailability of oral etoposide may be attributable to the immediate precipitation of etoposide in aqueous environment, e.g. gastrointestinal fluid; and both references attempt to improve etoposide oral bioavailability by delaying the onset of etoposide precipitation, the former by the addition of taurocholic acid to etoposide solution and the latter by addition of a water-soluble cellulose ether derivative or polyvinylpyrrolidinone.
It has also been suggested that an oral dose twice as high as an IV dose be administered in order to achieve the equivalent blood level (Stewart, D. J., loc. cit.). When high oral does is to be given in capsule dosage form, it is decidedly advantageous to have a concentrated solution of etoposide suitable for encapsulation within a soft or hard gelatin capsule. Such a concentrated solution will enable the preparation of capsules of smaller sizes thereby allowing for easier ingestion; it may also reduce the number of capsules to be swallowed. These factors can become important especially in view of the generally poor physical condition of cancer patients. The currently marketed etoposide solution having 20 mg/ml etoposide activity may be too dilute for the preparation of a convenient capsule dosage form.
Dimethylisosorbide (DMI) has been used as solvent for tetracyclines (U.S. Pat. No. 3,219,529), muscle relaxants (U.S. Pat. No. 3,699,230), steroids (U.S. Pat. No. 4,082,881), and aspirin (U.S. Pat. No. 4,228,162). DMI is miscible with water, ethanol, propylene glycol, isopropyl myristate, diethyl ether, acetone, corn oil, cottonseed oil, etc., and has a very good toxicity profile.
An object of the present invention is to provide a solution of etoposide in DMI. A concentrated solution is particularly suited as filling solution for gelatin capsules. The solution may also be formulated for parenteral use providing an elegant alternative to the complex multicomponent product currently being marketed.